1. Field
This disclosure relates generally to voltage regulators, and more specifically, to low drop-out (LDO) voltage regulators.
2. Related Art
A low drop-out voltage regulator provides a stable DC voltage. The input-to-output voltage difference of an LDO voltage regulator is typically low. The operation of the circuit is based on feeding back an amplified error signal. The error signal is used to control output current flow of a pass device, such as a power transistor, driving a load. A drop-out voltage is the minimum amount the input voltage must be above the desired output voltage to maintain regulation of the output voltage.
The low drop-out nature of the regulator is appropriate for use in many applications such as automotive, portable, and industrial applications. Other regulators, such as DC-DC converters and switching regulators, may not be appropriate. In the automotive industry, the low drop-out voltage is useful during cold-crank conditions where an automobile's battery voltage can be below 6V. Increasing demand for LDO voltage regulators is also apparent in mobile battery operated products, such as cellular phones, pagers, camera recorders and laptop computers, where the LDO voltage regulator typically regulates under low voltage conditions with a reduced voltage drop.
A conventional LDO voltage regulator uses a buffer amplifier, a differential amplifier pair, an intermediate stage transistor, a pass device coupled to an external bypass capacitor, and a high pass filter in a feedback loop. In this type of regulator, the capacitor used for the high pass filter is directly connected to an external pin of the integrated circuit. Because of this external connection, both capacitors rated at higher voltages and additional electrostatic discharge protection circuitry may be necessary. The buffer amplifier at the input of the regulator uses a high gain to reduce crosstalk between amplifiers and a high bandwidth to create a high bandwidth regulator, which may result in higher current consumption and increased die size.